An Overview of PicoRadio and Smart Dust

KD Kang

PicoRadio Sensor networks collect and

disseminate wide ranges of environmental data

Size, weight, cost & power consumption matter < 1cm3, < 100mg, < $1, < 1uw Bluetooth > $10 & 100mw Range of a Pico node < 2m Self-configuring ad hoc networking is a

must Multihop routing

Main Properties of Sensor Networks – PicoRadio View

Low sensor data rates Active duty cycle < 1% Location info make things simple Content- and location-based

addressing

Protocol Support Physical Layer

Mudulation Coding & decoding

MAC Layer Avoid message intereference

Network Layer Determines the path for packet delivery

Multihop networks

Energy consumption proportion to r4

Use several short intermediate hops Communication cost dominates

Communication-computation trade-off

Energy trade-offs

Network discovery & maintenance may consume more energy than actual data transmissions Proactive routing Reactive routing Hybrid, e.g., directed diffusion

Energy trade-offs

Standby power Send & receive consume a lot of power,

but Low data rate Careful medium access control

Separate potentially conflicting transmissions in time and frequency/code domain More complex radio???

Dynamic voltage scheduling

Power consumption proportional to V2

Aggressively reduce the voltage Careful!

Turn-on takes time & power More efficient physical layer

Application semantics

Radio power saving Frequency

Broadband Frequency hopping

Time Spreading Time synchronization required

Spatial Multiple antennas More expensive HW More antenna power consumption

Energy Harvesting

Smart Dust

KD Kang

Objective A few cubic “milimeter” size No more than 10 uw power consumption Float in the air Swallow to examine your body RF not viable

Limited space for antenna High frequency Excessive power consumption

Optical transmission Requires much less power than RF when a LOS is

available Space-division multiplexing necessary

Key ideas

Passive optical transmission techniques

Dust modes do not emit light Use CCR (corner-cube retroreflector) Requires an uninterrupted LOS Inherently directional

Active transmitters

Enable peer-to-peer communication between dust motes

High power consumption Used for short duration burst-mode

communication How to aim the beam toward the

receiving part?

Collision problems

Uplink collisions May not be serious if

Dust motes are sufficiently separated Transmissions are detected by different

pixels

Collisions due to peer-to-peer communications can be more serious